Friday, October 24, 2014

First Freeze, Last Freeze

When is the average first freeze date for Reno? I was thinking about this last week because I am a huge weather nerd, AND I felt like it should be coming up or here by now. I was correct. Table 1 below shows the average last freeze, first freeze dates for Reno, South Lake Tahoe, and Truckee. I know it seems backward to have last freeze earlier in the year, but this is based on the last freeze of the spring compared to the first freeze in fall or late summer.

Table 1: Listing the average last freeze and first freeze dates and the average number of days between the two for Reno (Reno-Tahoe Airport), South Lake Tahoe (South Lake Tahoe Airport), and Truckee (Donner State Park). Using ACIS data.

This year has obviously been warm and dry, hence the worsening drought. Minimum temperatures in the region have averaged 2-6°F above normal since our last freeze. Table 2 (below) displays Reno's record stretch without a freeze and South Lake Tahoe's and Truckee's near record stretches.

Table 2: Listing 2014's last freeze and first freeze dates, the average number of days between the two, and the all time rank in recorded history for Reno (Reno-Tahoe Airport), South Lake Tahoe (South Lake Tahoe Airport), and Truckee (Donner State Park). Using ACIS data.

Reno is about a month overdue for its first freeze similar to what South Lake Tahoe and Truckee experienced earlier this year. The last freeze occurred about 2-3 weeks earlier than normal for South Lake Tahoe and Truckee and nearly 7 weeks early for Reno. Reno set a record this year with the earliest last freeze on April 5th, and it is approaching the record for latest first freeze of November 3rd.

Our best chance for a freeze is Sunday night in Reno, but if that does not happen we will have to wait another 5-7 days before we get another chance with the current models' solutions. If it does freeze Sunday night in Reno, 205 days without a freeze would beat the previous record of 193 days in 1992 by nearly 2 weeks.

When examining hard freezes, temperatures 28°F or below, 2014 currently ranks 13th (204 days) in Reno's history (back to 1937). If we do not get to 28°F or below Sunday night then 2014 would assuredly be in the top 10 for longest stretches without a freeze and approaching the top 5 (218 days). The all-time record without a hard freeze was set in 2004 when Reno had it's earliest last freeze (March 4th) in recorded history.

So hopefully your gardens enjoyed this stretch of warm weather and the relatively wet warm season (May through September) we had in Reno (119% of normal precipitation). This reminds me of an old-Midwest wise tale about snowfall. The first time you received more than 3" of snow in November, that date was the number of snowfalls you would have for the rest of the winter. It held up relatively well, and let's hope a delayed start to our fall and winter will see the Sierra turn a corner for colder and wetter weather.